I'm having trouble with the PET program on page 14 in Issue 23, April, 1982. I couldn't get it to work. Now that I have looked at lines 140 and 150, I'm confused. Isn't [the variable] "TI" always zero? If so...doesn't this cause line 150 just to loop? At least that's where my program gets stuck.

Guy Lillis

The program you refer to is a "fast-find" for cassettes, but is designed to work only on Commodore cassette drives (PET/CBM/VIC). Programs which use only the keyboard or screen can usually work (with some changes) on most computers using BASIC. However, techniques involving peripherals like tape drives tend not to be very "portable" between computer brands.

For example, the Commodore machines have a special variable called TI (for TIme) which is an internal clock. This variable is always being updated by the computer and can, therefore, be used to time events. In your computer, TI is an ordinary variable, always zero unless you assign a value to it.

The "fast-find" technique is so specific to the machinery involved that it even needs adaptations to work on the different models of the Commodore line. (See the following letter.)